TURIN – There was a moment on Sunday night when Rafael Nadal was suddenly Rafael Nadal again.

This was during the first set of his first match at the ATP Finals, where he entered as the top seed, even though he had played only one singles match since his September loss at the US Open.

The whole sequence took roughly four seconds – a chase from deep in the backcourt to catch a drop shot from American Taylor Fritz near the net just before the second bounce, followed by a ridiculous, backhanded snap overhead hit on the sharpest of angles.

Cue Nadal’s signature hop-skip and roundhouse fist-pump, and a roaring crowd.

Members of his overflowing player box, which included his parents, coach Carlos Moya, sister, wife, agent and a few others, leapt from their seats, screaming “Vamos”, still thrilled by their boy wonder after all these years.

The moment was fleeting, though. Within the hour, Fritz was drilling Nadal, riding the momentum of winning the first-set tiebreak and his nearly untouchable first serve to prevail 7-6 (7-3), 6-1.

For a third consecutive match, Nadal, a 22-time Grand Slam champion, had lost to a member of the so-called next generation of Americans, a bizarre streak for him and another disquieting detail at the end of a year that included a back-from-the-dead revival and his first child, but yet another series of unsettling injuries.

“Six tough months in all ways,” Nadal said on Tuesday, after losing his second match of the tournament against Felix Auger-Aliassime.

By the end of the Fritz match on Sunday, Nadal, known for never losing his temper or giving up, was whacking balls across the court after his errors and half-heartedly swatting some of his final shots, seemingly accepting that defeat was inevitable.

There was more frustration on Tuesday afternoon, when Nadal once more showed glimpses of the old magic, the searing forehands and rifling backhands.

But too often in the crucial moments against Auger-Aliassime, the rising Canadian, he either found himself playing defence or making sloppy errors that betrayed his inactivity – just eight singles matches since July.

Playing him for the third time on tour, Auger-Aliassime cruised to his first win against Nadal 6-3, 6-4, ending Nadal’s hopes to advance past the round-robin phase.

Young players, who once crumpled when they saw Nadal across the net, has sensed his vulnerability.

“I felt like I had a really good chance of winning,” Fritz said.

Auger-Aliassime, who has won three tournaments this autumn, said his confidence grew as he and Nadal traded service games in the first set.

“I was like, ‘Look, I have a real chance of winning this’, ” he said. “I definitely believed that I could win.”

A few days earlier, Fritz had made Nadal feel things he rarely has against someone other than Novak Djokovic – rushed and under pressure, as if somehow Fritz had all the time in the world to do whatever he wanted with his shots while Nadal had no time at all.

“Everything was going so fast,” Nadal said on Sunday.

He tried to slow things down on Tuesday, drifting farther behind the baseline but that just allowed the powerful Auger-Aliassime to push forward.

In some ways, the sense of being short on time has pervaded Nadal’s entire year in ways both big and small.

At 36, he knows the end of his career is not far off, that every appearance at an event might be his last go-round there.

So does his family, which might help explain why his box is so full in Turin, just a few weeks after the birth of his first child, and how downcast they became as the matches wore on, though they yelled “Vamos” to the end.

Ageing and ailing physique and new baby aside, he has not lost his desire.

“I don’t know if I’m going to reach that level again,” Nadal said. “But what I don’t have is any doubt that I’m going to die for it.” NYTIMES